Fuel consumption

[mainshiptom]

Could this be true? Taken from MBM oct1988 boat report of the Westerly White water 46?

RPM Knots GPH LPH MPG RANGE
1000 9.3 5.2 23.4 2.48 996

Well if it is that is the speed I will be doing once Diesel price is up or on long journeys when range is important.

The acceleration is 0-20 Knots, 10 secs? But I will not be trying it out,

Tom

 

[Whitelighter]

Sounds about right for displacement speed.

 

[peterb26]

Sounds reasonable to me - the only thing is that 1000rpm might be just a bit on the slow side for long running.

Maybe 1300-1500 rpm would be better but it doesnt say what engines and what the rev range is.

 

[peterb26]

We are in agreement again Jez!

 

[Whitelighter]

It is becoming a habit. Shall we have a fight just to restore order??? /forums/images/graemlins/wink.gif

 

[mainshiptom]

RPM Knots GPH LPH MPG RANGE
1000 9.3 5.2 23.4 2.48 996

1200 10.1 7.9 35.6 1.29 520
1400 11.2 9.5 42.7 1.22 472

Tom

 

[rickp]

I'd always take the magazine figures with a large pinch of salt, as I think that in most cases (ie. where EDC-type controls or an actual consumption meter are not fitted), they base them from the engine graphs.

Still on a semi-displacement boat - the harder you push the loud sticks, the worse the mpg as there's no way to get over the hump....

Rick

 

[longjohnsilver]

Don't believe those figures, they were almost certainly taken from a graph from the engine manufacturers. Halving of fuel consumption for an extra 0.8kt doesn't sound right to me.

Most fuel efficient will be just below max displacement speed which should be about 8kts for the Wolfe.

 

[Chas25]

Assuming something in the region of 2500L tank range sounds right!

Not sure I'd want the bill for that though!! /forums/images/graemlins/blush.gif

 

[mainshiptom]

The fuel tank is 1800liters.
tom

 

[Divemaster1]

Irrespective of what the figures say, you ought to ensure you'd get a good working temperature on the engines, and suspect 1000 RPM is a bit on the low side for that..

My guess is that you'd need about 1300 RPM on those CAT's to get that, but you'll also ought to check at which RPM your turbos' kick in. (mine does at 1250).

Will do about 100 NM over the WE and if the wind is as gentle as today and the weather forecast indicates, we'll do those at 1300 - 1350 to measure the true displacement speed fuel consumption on our boat.

 

[thefatlady]

There's something wrong with the sums.

1000 rpm 9.3/5.2 = 1.79 mpg
1200 rpm 10.1/7.9 = 1.28 mpg
1400 rpm 11.2/9.5 = 1.18 mpg

 

[Andrew_Fanner]

>>>
you ought to ensure you'd get a good working temperature on the engines,
>>>
Carefully calibrated restriction in the raw water inlet perhaps? Or a bypass between impeller pump and exhaust?

 

[mainshiptom]

Can i fit a lower temp stat?

Tom

 

[Divemaster1]

[quoteCarefully calibrated restriction in the raw water inlet perhaps? Or a bypass between impeller pump and exhaust?

[/ QUOTE ]
Think I'd be careful to put any restrictions on the raw water intake side of the pump... do not want to generate additional stress on the impeller. Guess it would be better to have a bypass after and to the exhaust... but would need good non-return valves for the potential back pressure from the exhaust.... or perhaps even better a venturi effekt into the exhaust.... Need to be careful here so that this does not become a suction or "easy way" for the raw water, which may reduce the cooling to the extent that you'll overheat the engines.. /forums/images/graemlins/tongue.gif

Never thought about this as I'll never run more than a couple of hours at idle with load (450 RPM)

 

[Chas25]

Doesn't sound right then...

996miles/9.3knts = 107 hours x 23.4LPH = 2506 litres so 700l more than you've got /forums/images/graemlins/confused.gif

Working the other way

1800l/23.4LPH = 77 hours x 9.3knts = 715 mile range

 

[mainshiptom]

Should I sue MBM?

 

[mainshiptom]

Alf

Software working a treat with gps dongle !

Anything I can check on the cats while I am down there? We are taking an oil sample and send that away for testing, The engine room looks very tidy and clean I am not used to that,

Thanks

Tom

 

[Divemaster1]

You're welcome !

Oil sample to be taken just after engine run for quite some time at operating temperature. Would be good on old oil ... be aware if oil just have been changed ... if so, you should have a couple of hours run.

Run the engines under load for prolonged period (1hr + if you can) make note of Temp and Oil Pressure... then run WOT and watch temperature and Oil Pressure... see the increase in temp and note down .... should stabilise and not head for a continued increase in temp... if so, you may need a cooling system flush ... (approx £35 from CAT supplier for fast acting agent ... can get you the part no if you want).... Note where the Temp and Oil Pressure stabilises at WOT and reduce RPM to Cruise. Temp and pressure should now quicly settle at pre-WOT level...

Make sure you get the recommended WOT RPM ... otherwise over propped, or something else wrong. (may be seperate mechanical gauges for RPM, Oil Pressure, Temp and Gear Oil Pressure in Lazarette or Engine room, so check for Operation and reading between Engine Room, Helm and Flybridge)

At 375 and below, those CAT's should be good and reliable lumps of Iron and parts are readily available. Watch air seps or filters (if installed) ... these engines likes clean air.... as do most diesels as you know, so check blowers/vents etc. in engine room. Bring some CAT 3 hearing protection and stick your head in engine room at cruise RPM and at WOT.... should be a nice and even hum from the lumps.... take your time and watch and listen ... never mind the others onboard... this is the expensive part of the boat, so you want to see it operating well and that there are no oil leaks or things vibrating loose down there. Should be guards around fan belts = good, but make sure that the belts are OK, as guards will be extra job to remove if you have to change at sea ... so look at how guard is fastened.

Check when valves was last adjusted ... and if injectors were done at same time. Spin on filters or canisters? Racor Water Seps, or others?

Rest is routine really ... should be little smoke at startup, which should be very rapid if on a 24V system... may hunt for 5 sec ... and settle. If more than 15 sec., I'd suspect injectors or valves needing adjustement. White smoke @ startup = unburnt fuel = OK ... should not be Vo..o black, and should disappear after no more than 30 sec. running.

 

[Divemaster1]

[ QUOTE ]
Will do about 100 NM over the WE and if the wind is as gentle as today and the weather forecast indicates, we'll do those at 1300 - 1350 to measure the true displacement speed fuel consumption on our boat.

[/ QUOTE ]

Well, we did do that, but with a force 5-7 on our bow on Saturday, it did become somewhat lumpy .... bud did only do the first leg (5hrs) at about 1350 RPM, which I now believe may have been a bit on the high side as the 45ft hull (guess about 40 ft waterline) does just about 10.5 knot at 1400 RPM. My engines are rated approximately as the CAT's in the Whitewater Wolfe at about 385 ea., but run with a different torque and propellor curve.

In the F 5-7 head on sea (round Rattray Head up here), we averaged 45L per hour at approx 1350 RPM, which is not too far off the figures stipulated in your report. I think that our maximum range, whilst having the engines run sweet and warm, would be acheived approx 100 RPM lower at 1250 RPM, but need some time to validate this.... but will hope to do so in better conditions than what we had on Saturday. /forums/images/graemlins/smile.gif